This invention is directed to a polyarylate molding composition having improved notched izod impact values after molding. The impact modified polyarylate composition of this invention comprises a polyarylate derived from a dihydric phenol and an aromatic dicarboxylic acid, a polyester derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, and an aromatic dicarboxylic acid, and an impact modifier which is a graft copolymer of a vinyl aromatic, an acrylate, an unsaturated nitrile, or mixtures thereof, grafted onto an unsaturated elastomeric backbone and having a tensile modulus of less than about 100,000 psi. Additionally, said composition can include decarbromodiphenyl oxide.
Polyarylates are aromatic polyesters derived from a dihydric phenol, particularly 2,2-bis-(4-hydroxyphenyl)propane (also identified as Bisphenol-A) and an aromatic dicarboxylic acid, particularly mixtures of terephthalic and isophthalic acids.
Polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties. They have a high continuous use temperature of about 130.degree. C., and good unnotched toughness, with a pendulum impact value of greater than 300 ft. lbs./in..sup.3. Additionally, polyarylates have inherent flammability and combustion resistance as well as good weatherability. The polyarylates have good melt stability at high temperatures and good color retention. They also have good processability which allows them to be molded into a variety of articles.
In terms of their thermal and mechanical properties, polyarylates are comparable to other high performance thermoplastic polymers, such as polycarbonates. However, while polyarylates have excellent unnotched izod impact values (no-break), their notched izod impact values are considerably lower than polycarbonates, which have a notched izod impact value of about 16 ft. lbs./in. of notch. Thus, it is desirable to increase the notched izod impact values of polyarylate compositions, without essentially effecting the other mechanical properties of the polyarylates so that the polyarylates can be used in applications where high notched izod impact values are necessary.
The impact properties of polymers have been increased by the addition of impact modifiers. A wide variety of impact modifiers, based on rubbers of polybutadiene, butadiene-styrene copolymers, etc., as well as hydrocarbon based elastomers have been suggested as additives to thermoplastic polymers to increase the impact properties of thermoplastic polymers in general. V. Shahajpal, in "Developments in PVC Technology" edited by J. H. L. Henson and A. Whelan, Applied Science Publishers Ltd., New York, 1973, describes the use of impact modifiers which include graft copolymers of vinyl aromatics, acrylates and acrylonitriles grafted onto an unsaturated elastomeric backbone to increase the impact properties of poly(vinyl chloride). However, in comparison to polymers such as poly(vinylchloride), polyarylates have a high molding temperature (&gt;330.degree. C.) so that most impact modifiers, including the butadiene based elastomers, as described in said reference, degrade when processed at these high molding temperatures.
Accordingly, such impact modifiers are not suitable for use in unmodified polyarylates.
Additionally, a blend of the impact modifiers, as described in said reference, with certain polyesters, i.e., poly(ethylene terephthalate) results in only marginal increases in notched izod impact values.
Thus, it was unexpected that impact modifiers used in poly(vinyl chloride) polymers could be used to impact modify polyarylate compositions. Also, it was unexpected that these impact modifiers act synergistically with a blend of a polyarylate derived from a dihydric phenol and an aromatic dicarboxylic acid and a polyester derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, and an aromatic dicarboxylic acid, to provide a composition having high notched izod impact values after molding.
Additionally, decabromodiphenyl oxide is widely used as a flame retardant in polymeric systems. Decabromodiphenyl oxide has a rigid structure. Additives with such a rigid structure are commonly referred to as antiplasticizers since their addition to glassy polymers, including polyarylates, results in an increase in tensile modulus and strength and a decrease in izod impact values.
The addition of decabromodiphenyl oxide to a blend of polyarylate, a polyester derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, and an aromatic dicarboxylic acid, and the impact modifiers as herein described, results in an increase in tensile modulus and strength and flame retardant properties as expected. However, the notched izod impact values of the composition are not decreased as would be expected, but surprisingly, the notched izod impact values increase in most instances.
Accordingly, it has now been found that the notched izod impact values of polyarylate molding compositions can be increased by blending the polyarylate and a polyester derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, and an aromatic dicarboxylic acid with an impact modifier which is a graft copolymer of a vinyl aromatic, an acrylate, an unsaturated nitrile, or mixtures thereof, grafted onto an unsaturated backbone and having a tensile modulus of less than about 100,000 psi. Further, the addition of decabromodiphenyl oxide to such a composition does not decrease the notched izod impact values (as would be expected) and in some instances the notched izod impact values are increased.